Fuse



Dec. 29, 1936. H A TRIPLE-Vr 2,066,129

FUSE

Filed May 8, 1933 5 Sheets-Sheet 2 Dec. 29, 1936. H. AQ TRlpLTT 2,066,129

FUS E Filed May 8, 1935 5 Sheets-Sheet '5 Dec. Z9, 1936. H. A. TRlPLETT FUSE Filed May 8, 1955 5 Sheets-$11691'l 4 Dec. 29, 1936. H. A. TRIPLETT FUSE Filed May 8, 1935 5 Sheets-Sheet 5 QARTZ.

Inf/en Z909@- Patented Dec. 29, 1936 Y UNITED STATES PATENT OFFICE FUSE Hugh A. Trlplett, Wilmette, Ill., assignor to Schweitzer Conrad, Inc., Chicago, Ill., a corporation of Delaware Application May 8, 1933, Serial No. 669,955

82 Claims. (Cl. 200-120) My invention relates to electrical circuit procurrent flow rising to excessive or destructive tective devices which are generally termed fuses. values.

While the preferred embodiment herein dis- 1. Increase in resistance of the fuse link by closed is particularly applicable to use in high excessive current flow, and a cumulative heattension circuits, that is, circuits employing volting, resulting in fusion or melting of the metal. 5

ages suitable for transmission or distribution of 2. Vaporization of the metal of the fuse and electrical power, it is not intended to limit the the formation of an arc. invention to a particular use or voltage, the em- 3. Deionization of the arc by some action bodiments herein given. being illustrative and which intenupts the continuity of the current not limiting. flow. l0

The utility of devices of this general class is 4. Interposition between the fuse terminals of to interrupt current flow when the same bea dielectric of a value high enough that restrikcomes excessive. An electrical fuse is designed t0 ing of the arc by a resurgent voltage will not ocdepend for its action upon the heat evolved by cur.V

r current flow through a resistance. Heat is the In the Schweitzer 8: Conrad fuse, separation of 15 safest criterion of excessive current ilow because the fuse terminals begins as soon as the fuse is is the ultimately destructive force released by melted in the first stage above mentioned. such excessive current ilow. With fuses operating according to the aforeiuses, as heretofore known and constructed, said mode of operation, the current ow that have had a twofold function, iirst, to respond in can occur during part or all of the stages of the 20 a particular way as, for example, by fusion, that existence of the arc is limited only by the cais, melting, when the current ilow rises above a pacity of the connected system and the reactance predetermined value, and second, causing or perwhich remains in the circuit. As the connected mitting the substitution of an insulating medicapacity of the system is often very large, and um for the conducting link upon the occurrence the retained reactance small, the value of current 25 of the aforesaid response. flow through the arc occurring at the peak of The melting of a fusible link, according to the the current Wave sometimes rises to very high general practice in devices of this character, provalues. ceeds to the vaporization of the metal of the link There are also known the so-called powder l 3o and the formation of an arc. Whereas a solid filled cartridge .fuses in which the interruption 30 metallic conductor will increase .in resistance of current iiow occurs without movement ci the .as the temperature rises, and thereby tends to terminals and. consequently without the fourth reduce the current flow, I ilnd that as soon as step above mentioned, namely, the positive inthe metal passes into the vapor form and the terposition of a different medium between the :te current is conducted therethrough in the nature terminals in substitution of the metallic link. oi an arc, the resistance to current flow is great- In commercial forms of powder-filled there ly reduced. 'Why this is true'I am not at presis the disadvantage that upon operation of the ont able to say, but assume that it is due to the device no definite or marked change in the pogrcater crcssmsectional area of the conductor, sitions of the parts occurs, with resulting relau 40 that is, the metallic vapor, and the relatively tive uncertainty as to the ability to avoid punc- 40 greater freedom of the ionized particles; or p0S- ture, by the rise of voltage upon interruption of sibly greater freedom of the electrons to conduct current flow. Such fuses, furthermore, have the current, disadvantage, upon high tension circuits, that the In known forms of high tension fuses it has length of the fusible element must be so great been found desirable to deionize, or render inert, that a serious problem is presented in finding 45 the metallic vapors, or to expel the same from room for the necessary electrostatic clearance. the space between the terminals and finally to If the fusible conductoris subject to permanent interpose, as soon as possible, a high value dichange in its carrying capacity Without definite electric between the fuse terminals after the fuse blowing, as when it is required to withstand curm blows. rent flow close to its rating or is subjected to 5 The Schu/citeer fr Conrad high tension fuse is momentary overloads then its rating may be an example of a device now in general use. In changed without operation, and the functioning the operation of this device, as in devices of a. of the device becomes unreliable. This undesir- M generally similar character, there are four stages able characteristic, while it constitutes a parci' action brought about upon the @@Currenee of ticul'ar dimculty for powder nlled fuses, will be 5 present more or less in any fuse unless special provisions are made to overcome it.

It is the chief object of the present invention to provide a current interrupting device involving, in the preferred form, a fusible link, which device shall provide means to avoid the high peaks of current fiow in the system or bring them down to a value where the arc at the fusible link may easily be extinguished.

It is another object of the invention to provide a device which has two distinct cooperating elements, one a fusible link designed to have characteristics favorable to its function of providing and maintaining a definite rating to which it responds, and the other a self-altering conductor designed to be insensitive to current flow of a value equal to the rating of the fuse but capable of reacting vigorously for currents substantially in excess of said fuse rating, to increase its resistance rapidly and in a very pronounced degree.

I am aware that it is old to insert a fixed pro tective resistance in series with a transformer fuse or other fuse of relatively low capacity, such as may be employed in instrument circuits. Such protective resistances limit the maximum current iiow, rst, by their resistance value at normal temperature, and second, by the increase in resistance due to the heating under excessive current flow.

Such protective resistances, in order to be of appreciable effect, must be of such a high value that they definitely obstruct current flow of any value. For instrument circuitsand the like, the current flow is so small in value that the energy loss is not important, but in power circuits the loss in energy would be so great as to make the problem of dissipation of the resultant heat serious, and the loss of energy would also become serious. Hence, the employment of a fixed current limiting resistance in series with a power carrying fuse or fusible device has not been practiced.

It is one of the chief objects of the present invention to provide a protective device in which an automatic current limiting resistance of the self-altering type is employed for limiting the maximum current flow, for use both in low current fuses such as employed for instrument work, and in fuses of larger rating, such as are employed for power current transmitting purposes. The energy release in the system is thereby controlled and is kept low.

I have conceived the possibility of providing a circuit protective device in which a fuse element with a fusible link is employed in correlation with a resistance element having an automatically increasable resistor, normally of low value, but adapted, when the current flow through the device increases at a rate which presages a high peak value', of permanently increasing its value so greatly as to limit the current flow to a value which permits the fuse element to disconnect the circuit. The increase of the included resistance may be so great as to reduce the current flow to zero. However, in the preferred embodiment of my invention, the fuse element has a movable member performing the function of interposing a definite gap in the circuit, under any condition of operation of the device.

The device of my invention has selective modes of operation for different conditions of current increase therethrough, as I shall here briefly explain. A fuse such as the Schweitzer 8: Conrad fuse has a definite action when the current ow increases to a value which causes the fuse to melt. When the fuse melts, the retractile spring takes control and separates the fuse terminals and brings the arc extinguishing medium into play.

The oxidizable or otherwise self-altering resistance of the present invention acts differently. It is not intended to establish an arc under any condition. Its initial resistance in the present device is relatively low. It is not designed to act until the current flow reaches a value substantially in excess of that at which the fuse blows.

If the rate of current increase through the device is relatively low, the current flow may be interrupted at the fuse link with little, if any, permanent change in the resistor.

If the fault current is low, the device may operate by yielding of the fusible link and extinguishment of the arc which ensues at this point, without calling the automatic resistance into play. This action may occur with or without removal of the cap by the action of extinguishing the arc according to the usual operation of fuses.

The resistor, in oxidizing or otherwise altering itself, acts quantitatively and cumulatively. If the rate of increase of current flow through the device is high, so that it passes far beyond the rated value of the fuse, the action of the fuse element will be relatively ineffective as compared with the action of the self-altering resistor, which then takes control to limit the current flow to a value where the arc cannot be sustained and is extinguished and the movable terminal of the fuse can effect the disconnection or interposition of a gap of so great a value that restoring of the voltage Will not reestablish the aIC.

Thus, for low rates of current rise, the fuse may retain control, but on high rates of current rise the resistor alters its own value and takes control.

Where, as in one embodiment, the fuse element and resistance element are initially connected in the circuit in series, the movable terminal or terminals of the fuse serve to increase the length of the arc, inject an arc extinguishing medium, and to interpose the final disconnecting gap. Where, as in another embodiment, the fuse element and resistance element are disposed in parallel, the movable terminals have, in addition to the above function, the function of causing a shift in the current ow from the path including the fuse element to the path including the resistance.

In another embodiment, where the resistor is normally out of circuit, the movable terminal or terminals have the additional function of bring-` ing the resistor into circuit.

In all the embodiments herein disclosed it is intended that if the fault current be low, Athe device shall clear the circuit at the fusible element. In that case the fusible element yields, the arc is formed, and is extinguished, with or without. blowing of the cap, but without calling the automatic self-altering resistance into action.

This is possible because the fusible element fuse is designed and constructed to melt its rating, which is also the rating of the device. Now, although the fusible section designed to melt when its rated blowing current is reached, the current may continue to increase to an ini-- mensely greater value during arcing at the gap.

It this should occur, it would put an enormous duty upon the fuse which would create an excessive disturbance and a possible failure. But the self-altering resistor, which is so designed or connected as not in anywise to be affected by the mere rated current of the fuse, comes into operation either because it is in permanent series connection, or because it is switched into the circuit either in series or parallel in a decisive manner when the current rises beyond the value at which the fuse is intended toblow, and promptly alters its resistance, thereby relieving the fuse of excessve duty. The reason that the self-altering resistor, when permanently connected in series in the circuit, does not act at the current value which melts the fuse is that the resistor is designed to carry a current which will melt the fuse without heating up to a temperature which will initiate the chemical reaction. But as the current goes to a value which heats the resistor to a temperature at which the reaction begins, the resistor alters its conductivity. The more it reduces its conductivity the higher its resistance rises, and the hotter it tends to become. 'I'he action thus is cumulatively accelerated. In those cases when the resistor is normally not in the circuit, but is switched into the circuit either in parallel or in series with the arc or a part of the arc, it is saved from deterioration by the fact that it is not subjected to current flow until the fuse melts.

The device thus includes the combination of fuse element and resistance element connected either in series or parallel arrangement, in either a permanent manner or in a manner to be automatically switched into the circuit upon the necessity for the same arising.

The fuse clement, when it operates, introduces a permanent gap in the circuit, and the resistance element, when it operates, introduces a permanent increase in the resistance of the device.

The current limiting resistance element which I employ in the preferred form of my invention has the characteristic of increasing cumulatively its own resistance, not merely by the thermal coefliciency of resistance which is a property of the metal employed. but by a chemical union with a reagent which is liberated by the temperature attained by the element. This reaction, which produces a permanent change, reduces the element to a non-conductive form, preferably without arriving at the stage of forming free metal vapor as a part of the current carrying path.

With these two dissimilar' types of current responsive devices it is possible to secure current interruption within a device of relatively small dimensions and without the necessity for venting vapors or gases to atmosphere.

in fuses of the type which permit the fusion of the iink to proceed to vaporization of the metal and the establishment of an arc therethrough without control of the resistance of the circuit, there is always the possibility of the release of large amounts of energy in the form of heat, with resultant excessive iluid pressure. It is known to employ a deionizing agent which can be conducted into a separate chamber and to some extent hold down the pressure by condensing the vapors and gases. Nevertheless, the' tendency to evolve great pressure is present where the resistance of the circuit is uncontrolled. It

the resistance of the circuit can be adequately controlled before the rush of current reaches too high a value, then the violence of the arc, with resultant fluid pressure, can likewise be controlled, and special condensing chambers or undesirable venting of gases and vapors to atmosphere may be avoided.

The positive separation of the terminals of a device of this character, acting to interpose a definite dielectric medium, is highly desirable, particularly where, as in the preferred form of the present invention, a glass container is employed which gives the possibility'of visual inspection to determine the condition of the device. Such visual inspection of a gap in the circuit of the device is highly desirable.

There are numerous improvements in detail provided by the present invention. These will be apparent from the following specification and drawings.

Now in order to acquaint those skilled in the art with the manner of constructing and operating a device embodying my invention I shall describe, in connection with the accompanying drawings, a specific embodiment of the invention, and shall state its mode of operation.

In the drawings:

Figure 1 is a diagram illustrating the connection of the fuse, with the fusible element. the

operating spring, and the cooperating resistance` element in series;

Figure 2 is a similar diagram illustrating the connections of the form of device in which the resistor element is switched in upon blowing of the fusible element;

Figure 3 is a similar diagram showing the fusible element and the resistance element connected or switched in parallel;

Figure 4, shown in two parts, is a veri-ical longitudinal section through an embodiment of my invention. Part l shows the upper portion of the fuse, in section, and part 2 shows the lower portion of the fuse, in section;

Figure 5 is a diagram illustrative of the mode of operation of the device shown in Figures 1 and 4;

Figure 6, in two parts, is a vertical longitudinal section through a modified form of my invention, part 1 showing the upper portion of the fuse, in section, and part 2 showing the lower portion of the fuse, in section; Y

Figure '7 is a view similar to Figure 6, part 2, showing a modified arrangement of the lower portion of the device of either Figure l or Figure 6; I

Figure 8 is a cross-section of the device shown in Fig. 7, taken on the line 8-8 cf Figure 7:

Figure 9, two parts, is a longitud'nil vertical .w

section through another form of fuse embodying the connection shown in Figure 2. Part l. shows the upper part of the device, in section, and part 2 shows the lower part oi the device, in section;

Figure l0 is a vertical longitudinal section thrrugh a modified form of my invention, embodying the connection shown in Figure 3; and

Figure 11 is a sectional view of a modification of the fuse-containing tube, taken on line I I-ii of Figure 9, part l.

Referring now to the embodiment shown in Figures l and 4. I provide a completely enclosed element employing the enclosing sleeve i of glass.

@ther suitable insulating material may he emof the glass sleeve I there is mounted the ferrule 2 which forms an external terminal suitable for mounting in a spring clip or the like, for connection of the device in an external circuit. Similarly, the lower end of the sleeve I has a metal ferrule, closed at its lower end, this ferrule l being in the shape of a cap. The ferrules 2 and I are secured upon the ends of the glass or other insulating sleeve I by a suitable sealing alloy or compound 4, making a tight joint, mechanically and pneumatically. Between the upper ferrule 2 and the lower ferrule 3 there are connected two dissimilar current responsive elements, namely, the fuse element 5 and the resistance element 6. The fuse element 5 comprises a silver wire 1 which serves to conduct normal flow of current and to fuse upon the iiow of excess current. A

high tensile strength member 8, which is preferably of a nickel-chromium-alloy such as Nichrome or Chromel, sustains the pull exerted by the retracting spring 9. Its function is largely mechanical, as will be apparent later. The resistance element 6 comprises a tungsten wire I0 disposed in loose coils and surrounded by a cornpound which, upon being heated, releases a chemical reagent that combines with the substance of the wire I0 and causes it to become substantially or completely non-conductive. The compound I2 may be calcium carbonate, in the form of marble dust vor other suitable or equivalent material for performing the function which it is the purpose of the marble dust to perform. The silver wire 1, which is the fusible element proper, is sub,- stantially free of any deterioration due to heating to approximately its melting point. In other words, this element is designed to remain intact until current flow through it indicates such a release of energy in the connected circuit that thc entire device should operate to interrupt current flow. The resist-ance wire III, on the contrary, would be subjected to possible deterioration by a transient or temporary value of current flow in excess of normal, hence its purpose is to remain unchanged until the rate of energy release, i. e.. heating, indicates a low resistance fault in the circuit. The fusible wire 1 determines definitely when the device shall operate, by vaporizing and forming an arc. The resistance wire I0 has the property of increasing its resistance by current flow and, in addition, upon high rates of energy release, of evolving carbon dioxide or oxygen from the calcium carbonate and combining with the oxygen thereof to produce tungsten oxide, which is substantially non-conductive, and thereby permanently increasing its resistance to a point where it is substantially non-conductive in character, without the formation of an arc. Other compounds may be formed, but if so they are substantially non-conductive. The silver wire 1 tends, of course, to increase its resistance to current flow so long as it is increasing in temperature without melting, but this is of no appreciable or effective value. The silver wire 1 will melt at a temperature far below the melting point of the tungsten wire I0, although the current ls iiowing through the two wires in series. The effeet of a high increase in current flow on the resistance wire I0 is to cause it to increase in temperature up to the point of releasing carbon dioxide or oxygen from the compound I2 and itself becoming chemically active. The wire attains such a temperature 'as readily to combine with some of the constituents of the marble dust, to convert itself to a non-conductive oxide or other compound. The heating up and the consequent chemical reaction occur normally within a half cycle or less. Aa a result. the device is able to interrupt current ilow without allowing the liberation of much energy in the system. That is to say, the current ow is interrupted promptly, and without allowing the value o! current flow to reach peak values such as would occur without the limiting effect of the wire III.

In Figure 5 I have indicated the comparative effects of the present fuse and previously known forms of fuses for interrupting current flow upon the occurrence of a substantially dead shortcircuit. In Figure 5 the sine wave graph A indicates the impressed voltage upon the circuit protected by the device. The sine wave graph B indicates the voltage across the terminals of the device. The line C indicates the current flow through the device of Figs. l and 4. The horizontal portion of the line C indicates zero current. The light vertical lines D and E indicate the period of time during which short-circuit current was flowing. It is to be observed that the short-circuit was applied as the potential wave A passed through zero. This is the most severe condition. The peak of current ilow indicated at F reached approximately 600 amperes and the interruption occurred in an exceedingly short space of time, that is, lem than half of ahalf-cycle. As determined by the oscillograph, the circuit was interrupted in a period of time represented as 0.0026 second.

In previous forms of fuses in which the interruption has depended entirely upon extinguishment of current flow at the fusible conductor, such as the silver wire 1, the peak of current flow reaches a value indicated by the dotted line G, attaining a value of approximately 11,000 amperes and extending over a period of time approximately .014 second.

In such prior fuses extinction of the arc is not accomplished until the current wave passes through zero value. These zero values tend to occur at definitely timed intervals, i. e., twice per cycle` Hence, in such prior forms of circuit interrupters, the current has the opportunity to rise to a high peak, with the ability to release relatively great amounts of energy in the system. This time may be further extended by the shift in phase which may occur. Hence, a low resistance fault may cause serious damage to the connected apparatus, conductors, etc.

Now I shall describe in detail the structure of the device shown in Figures 1 and 4, which brings about the operation above described.

The silver fuse wire 'l is connected between a stationary terminal stud I3 and a movable ter- ,7,

minal stud I4. These terminal studs are slotted, the ends of the wire 1 laid thereinto and the edges of the slots battered over to embrace the corresponding parts of the fuse wire. The strain Wire 8 is anchored in bores in terminals I3 and I4, the ends of the strain wire being formed into loops with transverse pins extending through the saine. The mounting of the strain Wire 8 in the terminal studs I3 and I4 is disclosed in the copending application of N. J. Conrad, Serial No. 470,416, filed July 24, 1930, and forms no feature of the present invention. Sufiice it to say that the mounting gives the strain wire a suitable limited degree of universal motion.

The fuse wire 1 is coiled about the strain wire 8 and a body of cork I5, with an opening through the center of the same, embraces the terminals I3 and Il and encloses the fuse wire 1 and strain wire 8. The stud I3 is mounted upon a suitable spring spider I6 which is seated in a counterbore til) II and upon a shoulder I8 in the upper end of the ferrule 2. The upper end of the ferrule is closed by a releasable cap Ill which is held in place by a suitable cement, to give a definite holding value to retain pressure within the device up to a predetermined value. The container formed by the sleeve I and ierrules 1 and 3 is substantially lled with an arc extinguishing liquid 2B which may be a halogen derivative of a hydrocarbon. Any suitable arc extinguishing liquid or medium may be employed. The level oi' the liquid stands normally, when at room temperature, approximately at the line Y--Y. If the cork is pulled down, in operation, the level may rise to X--X. The movable terminal stud I4 carries the liquid director 22 for projecting a stream of the liquid 20 upon the tip I4 as the same descends after blowing of the fuse 5. The terminal stud I4 is secured by the screw 23 to the upper end of a tension spring 9 through the medium of a clamp 25. The lower end of the spring 9 is secured by a similar clamping plate 26 and screw TI to a stud 28 which is threaded into a terminal socket formed in the metal head 2! forming the upper part of the enclosure for the resistance wire III.

The enclosure for the resistance wire III and its nlling I2 comprises the Bakelized" ber sleeve t@ which has a longitudinal groove 32 extending the i'ull length thereof and two circumferential grooves, namel, 33 at the upper end and 34 at the lower end. The resistance wire I! is formed in a helical coil with the ends thereof extending axially and secured in head members -Jl or generally cylindrical form with extending threaded studs 36, as shown at the lower end. These studs are threaded into head members 31 mici 38. Each of the terminal members 35 has a .radially extending pin I9 acting as. a hey sliding in the slot or keyway S2 to prevent rotation. The heads 3l and 38 are guided in the ends of the sleeve l and at their inner ends are reduced in diameter to provide, in effect, a groove for receiving' a split wire ring IB48 preventing end- Wise movement.

The head members {I1-Ji have conical anges overhanging the ends of the sleeve 30 to provide stubstantially tight closure. The heads 31 and 3B are threaded down upon the studs 38 and the conical flanges act like puppet valves to close off the ends of the sleeve 30. As a result, the generation of gas pressure within the sleeve 3U may occur Without immediate transmission of 'the pressure to the inside ci the glass sleeve I,

The lower head 38 has an extending threaded t, sir-id 2 is threaded into a boss 43 on the inside oi the cap 3.

The operation of the device is as follows: assuming that current iow in excess of the rated pacity of the device occurs, if this excess is but zfmporary the silver fuse Wire l will carry the same without fusion and without deterioration by corrosion or scaling or the like. Practically all of the current flows through the wire l and very little through strain wire 8, since it is o1' high resistance. Il, however, the rise in current is sharp and pronounced, in the case of a short circuit, the temperature of the wire l rises rapidly. the current at a rate which corresponds to a low resistance i' uit in the system the fuse rapidly reaches the vaporlzing point, with immediate fusing of the Wire 8 and the formation of an. between the terminals I3 and I4, and a decrease in the resistance between the said terminals 53 and I4, The same current :door which extends through the arc extends in verted into tungsten oxide.

series through the tungsten wire I0 and the current iiow through the fuse and the ensuing arc causes heating of the tungsten wire I0. It is in contact with the marble dust I2, and since a. relatively low temperature only is required to calcine the marble dust it begins to give off carbon` dioxide at a temperature below the melting point of the tungsten wire. The tungsten wire continues to rise in temperature, reaching incandescence without losing its character as a solid.

At incandescence it is actively attacked by the oxygen released from the marble dust, being con'- This compound is substantially non-conductive. Other compoundsv may be formed. I am not able to say positively the exact reaction that occurs. It may be that the reactions are more complex than above indicated, and other products may be formed. They are, however, substantially non-conductive, so far as my tests indicate.

As soon as the fuse 5 has blown, the spring 9 is free to retract the terminal I4. However, the action of the tungsten wire Il in heating up and oxidizing is so rapid that it will be converted into a non-conductor before the terminal I4 has moved more than approximately A inch.l However, afterbeing once released, the terminal I4 continues to move with an accelerated motion and inasmuch as the resistance of the wire I0 begins to increase with great rapidity as soon as it has reached incandescence, the arc which might be maintained between the terminals I3 and I4 is extinguished quickly and without violence. As the terminal I4 recedes it is drawn under the liquid 20, which liquid, being of a high dielectric strength, interposes itself lin the gap between the terminals I3 and I4 and prevents striking back of the are, interposing a definite dielectric, and giv ing a visible indication of the fact that the fuse has opened the circuit.

The two elements, namely, the fuse 5 and the resistance 8, are of distinctly different character and each supplements the action oi' the other. The fuse element 5 determines when the device shall positively operate, whereas the element 6 .will act quantitatively when the value of current flow initiating its operation occurs. The element 5 operates to interpose a non-conductor by first forming a gaseous conductor, that is, an arc, but

the arc is kept under control both hy the extinff guishing mechanisms, namely, the smic It, liguiai director 22, and liquid dielectric 2t), as well as by the resistance member S. The two elements 5 and 6 are disposed at opposite ends of the casing so that each is out yoi the others influence to as great an extent as possible. That is to say, the arc which may occur at the .element 5 should be kept away from the resistance 6 and likewise it ,is desirable that any chemical action which might occur in connection with the element 6 should be kept away from the element 5. The carbon dioxide gas which is generated in the speciic combination of elements here disclosed has no adverse eiect, so far as I can determine upon the silver fuse wire "I nor the alloy strain wire 8. I-iow-l ever, the ingredients may be varied, and in that event the reagent which may be employed in connection with the element 6 might be detrimental to the element 5.

The embodiment shown in Figure 4 is particularly applicable for small values of normal our rent iiow, that is, the rating of the fuse is not in excess of 5 amperes. In such case the resistance ofthe tungsten wire I0 is of the order of 0.2 ohms.

The marble dust, or calcium carbonate, is inert at relatively low temperatures and it must be heated by the tungsten wire before it will release any reagent. The release of carbon dioxide by the heat of the tungsten wire is accomplishd without the marble dust passing through the vapor stage or without boiling of! any appreciable amount of the liquid which may find its way into the marble dust. Exclusion of the liquid dielectric from the inside of the sleeve 30 is desirable. The tungsten must be heated to a value of the order of 1400o C. before it becomes active in combination with the carbon dioxide or the oxygen released by the marble dust. In reaching this temperature it increases its resistance of the order of seven to ten times. Where other reagents are`used, or where a different composition of the wire with the same or a different reagent is used, the temperatures at which operation occurs may be different.

While I prefer to dispose the fuse 5 at the 0ppcsite end of the casing from the resistance l, and design each to perform its function out of the influence of the other, I do not wish to limit the arrangement to such separation, for the rfusible element may be made a direct continuation of the inusible resistance conductor I0, or disposed in close proximity to the same. The thing which is not desired is any interference between the action of the arc and the action of the conductor III.

The specific embodiments of the element 5, which contains the oxidizable or chemically combinable conductor Il), may be varied, as may the fuse member 5, which includes the vaporizable conductor 1.

In the embodiment of Figure 6 the fuse element 5a,as well as the resistance element ia, exhibits a modification in structure and individual mode of operation, but the cooperating action is as above described. The fuse element and the resistance element, 5a and 6a, respectively, are continuously connected in series in this embodiment.

The fuse 5a is constructed substantially as disclosed in the ccpending Patent No. 1,907,581, granted May 9,1933. The fusible element is a nickel-chromium-alloy wire of small diameter, indicated at Figure 6, part 1, by the reference numeral 50. The upper end of the fuse wire is connected to a terminal block 52, this terminal block having a threaded stud 53 extending upwardly through the spring spider member 54. The spring spider member comprises a plate having a hole through the center for receiving the stud 53 and has the spring fingers formed by slotting the flange as indicated at 55, these spring fingers engaging in the counterbore I1 and resting endwise upon the ledge or shoulder I8. A clamping nut 56 holds the block 52 against the bottom of the spider 54. At its lower end the silver fuse wire 50 is connected to a lever 51 pivoted at 58 between two plates of insulation 59. The free end of the lever 51 is connected to the fuse wire 50. A series of levers Bil, 60a and 50h are pivoted alternately upon opposite sides of the center line and rest upon each other, the lower lever 6012 resting upon the lever 51 to which the fuse Wire 50 is secured. A loop of high tensile strength wire or of sheet metal of adequate current carrying capacity is connected between 'the uppermost lever SII and the movable terminal 63. This loop 62 is made in the shape of an open link having an eye at each end. At the upper end the link rests upon the lever 61| and at its lower end 'the link is inserted in an axial opening in the movable terminal 6! and held in place by a cross-pin 5I. The plates of insulation l! are slotted to receive the link I2. The link l2 is not intended to be fusible. A barrier member or transverse plate 55 is threaded internally in the upper end of the ferrule 2 and it has a counterbore and shoulder 65 to receive the upper end of the tube 61 defining the arcing chamber. This tube 51 has a head or enlargement 6l resting in the counterbore of the barrier plate 55. The tube or sleeve of insulation 61 is held in place by a plurality of washers 59-69 overhanging the upper edge of the head 68 and secured in place by the pins 11|, which are pressed into the barrier plate or head member 85. Instead of a series of washers a single continuous ring or equivalent arrangement for holding the upper end of the arcing tube I1 in place may be employed.

The movable terminal 53 carries the liquid director 22, a series of pins 12 extending radially out from the movable terminal 63 and engaging in a groove in the liquid director 22. The liquid director 22 and the movable terminal 53 are telescoped with the lower end of the arcing chamber 51. The sleeve I is filled with arc extinguishing liquid which extends to approximately the level Zr-Z of Figure 6. part 1. The lower end of the movable terminal 63 is connected to the head 13 by a threaded stud 14. The tension spring 9 is connected to the spring head 13. 'I'he lower end of the spring head 12 has a socket 1I for re ceiving the flexible conductor 2l. A similar spring head 15, having the socket 1l for the flexible conductor 2l, is disposed at the opposite end of the spring. The head 15 is anchored to a terminal member 11 forming the upper end of the resistance member 5a, as by means 0f a suitable stud on the head member 15 and a socket in the terminal member 11.

'Ihe unit 6a comprises the upper head member 11 and the lower head member 1l, these head members having internally threaded sockets 15-19 and centrally disposed tapered studs III- 80, substantially alike in construction. The threaded sockets 19 receive the threaded ends of the sleeve l2, which is made of Bakelized fiber or like insulating material. The central projections ll, which are tapered at a relatively small angle, fit closely in the tapered sockets formed in the outer ends of the sleeve of insulation B2 to form substantially fluid-tight joints. A suitable sealing material may be employed in connection with the threads of the sockets 19 and the fit of the tapered plugs l0, so as to seal off the inside of the unit Sa from the outside thereof by fiuidftight seal. The projections -80 have central axial recesses in which are disposed springs 83-83 placed under compression to secure definite contact between the head members 11 and 1I and the corresponding terminal mem bers of the wire I0. The terminal members of wire I0 comprise sheet metal plates or discs M set in grooves 85--85 The compression of the springs 83-83 and the tension of the resistance wire I0 hold these discs or plates 84--84 expanded into the grooves 85-85 and thereby hold the same definitely in place. The interior of the sleeve 82 is filled with a filling of marble dust I2, or the like, and the wire I0 is made of tungsten or the like. The desideratum is to have a Wire of very high melting point which is capable, when it has reached a high temperature, of releasing a reagent from the compound I2, which reagent will combine with the substance of the wire Il to produce an insulating, or substantially non-conducting compound of the substance o! the wire i9.

The fuse shown'in Figure 6 is designed for very low current rating and it is for this reason that the fusible wire 59 is given the mechanical advantage over the spring -9. In point of overall operation the operation of the device shown in Figure 6 is like that described in connection with the device of Figure 4. Speciiically, the operation of the fuse element 5a corresponds to the mechanism therein disclosed. As soon as the current through the device has attained a value which softens or melts the fuse wire 99. the lowermost lever 51 is released, and progressiyely these concatenated levers releases the link 92, whereupon the spring 9 moves the terminal 93, with its connected link 92, downwardly. vThe arc which follows the rupturing of the fuse 9.9 is confined radially within the sleeve or ax'clng chamber 61, and the descent of the terminal 93 with the liquid director 22 projects liquid into the arcing chamber, tending to drive out the metal vapors through the upper end of the sleeve 91, to extinguish the arc. However, the cooperation between the fuse 5a and the resistance'wire i9 is as heretofore described. The wire i9 increases its lresistance by heating. When a temperature has been reached which re- 'leases the required chemical reagent from the compound i2, such reagent is freed and is in position and condition, to attack the material oi' the wire i9 as soon as it reaches the ignition temperature or the temperature at which itis chemically active. The wire |9 then burns to a non-conducting oxide with great rapidity. In fact, the action is accelerated.

Ti' not to say that the chemical reaction is altogether an oxidation of the tungsten. There may be other compounds formed, but the reaction is effective to produce the result desired, and whether the tungsten combines with the calcium in more or less degree, or whether the reaction is entirely an oxidation, I have not as yet been able to ascertain. I believe that the significant and useful reaction is oxidation.

The unit 9a is sealed air-tight by the application of a compound which is not dissolved in the arc extinguishing liquid with which the device is filled. The arc extinguishing `liquid continues into the lowermost part of the device in Figure 6 and completely surrounds the unit 6a.

In Figures 7 and 8 I have shown a modified embodiment of the resistance unit designated 9b. The upper end of the device, including the fuse, is identical with Figure 6, part 1, and therefore need not be described.

In the construction shown in Figures 7 and 8 the resistance unit 9b is provided ywith a vent to atmosphere. The upper terminal and ferrule member 9i is mounted upon 'the upper end oi the glass sleeve 89 by means of the sealing alloy d which is preferably the same alloy employed in sealing the upper andlower ferrules 1 and :i upon the main glass sleeve l.

The lower ferrule member 89 of the unit 9b is likewise sealed upon the lower end of the glass sleeve 99. The upper member 91 is imperiiorate, having a socket externally at its upper end for receiving the stud of the lower spring head 15, and is provided internally with a socket 99 for receiving the stud 92. This stud 92 is preferably in the form of a screw provided with a suitable screwdriver slot and having secured in its head the upper end of the resistance wire I9. The lower head and ferrule member 99 is perforated and has a counterbore 93 in which there is disposed a curved crossbar 94 forming a terminal for the lower end of the resistance wire I9. Said resistance wire has a hook-like extremity hooked over a crosspin 95 lying in a slot 96 in the bar 94.

i The lower ferrule member I on the main glass sleeve I is bored out to" provide a cylindrical guiding surface 91, which engages a corresponding cylindrical surface on the sleeve member 99 of the unit 9b. The main ferrule member 3 is threaded and counterbored to provide the surface 99 against which a corresponding enlargement of the sleeve member 99 of the unit ib engages and between the shoulders formed by the counterbore and the enlargement there is a space 99 which is illled with a suitable lsealing compound oi a. character which is not attacked by the liquid arc extinguishing material 29 which lls the main sleeve The outer sleeve member 9 has afurther counterbore |99 and the inner sleeve member 99 has a ange or head |92 for providing a positive endwise engagement between the ferrules 9 and 99. Adjacent the flange or enlargement |92 there is a groove |99 formed in the sleeve or ferrule member 99 and this groove is tilled'with a sealing compound which is unaiiected by moisture. Two different sealing compounds are used, the outer one t0 seal against moisture and the inner one to seal against the arc extinguishing liquid.v since each may thus be selected best to perform its function. The flange or head |92 of the inner sleeve 99 is` clamped in place by a screw plug |94 which is threaded into the open end of the ierrule 9 and clamps the flange |92. At the same time, a central stud |99 presses against the center of the crossbar or terminal member 91|, holding it definitely in place in its recess or counterbore 99. An annular disc or washer |91 lies in the annular recess -formed in the plug member |94, this disc or washer |91 being porous, and consisting preferably oi a soft brous material such as asbestos. Waterproof paper sheets |99 are disposed on opposite sides of the asbestos washer |91, or, ii' desired, the lower paper sealing washer alone may be employed, the upper one being omitted. Vent openings |95 extend through the lplug member |99, these vent openings permitting the escape of gas pressure from within the chamber in which the .resistance wire and its iiling material i2 are contained.

The inner walls ot the glass sleeve 99 may be lined with a material which will insulate the glass sleeve from the intense heat of` the wire i9. To this end a lining |99 of plaster o'i Paris may be cast in place. l

The operation of the unit shown in 6b is substantiaily identical with that of the resistance units 9 and 6a heretofore described. However, the interior of the unit 9b can vent to atmosphere through the asbestos washer |91 by rupturing the paper sealing disc or discs |99 and passing through the vent openings |99. This does not permit'escape of the arc extinguishing liquid since the unit 9b, although surrounded by the arc extinguishing liquid, has its interior completely sealed oi from said liquid.

The type of device above described has a numm ber oi distinct advantages'. It is old to employ a fixed resistor in series with a fuse, particularly fuses of low current carrying capacity, but where a iixed resistor is employed the resistance must be of a relatively high value to be oi any worth.

In a fuse for k. v. circuits, such as the devices above described, the short circuit current may rise to 10,000 to 15,000 amperes during the first haii-cycle if the fault is of low resistance. For a fixed resistor to have a suilicient limiting effect to prevent blowing of the cap of! of the fuse it must be of the order oi from to 480 ohms, de- `pending upon the voltage of the system. However, such a large amount of resistance is too `sullty to be incorporated in a fuse. By the provision of a resistor which automatically increases its resistance with current ilow, there is a highly desirable action. The IR loss may be made very low for normal current rlow, in view of the fact that the resistor is of low order. for example, 2/ 10 of an ohm. The choking effect of the automatic resistor being dependent upon current iiow therethrough, permits the resistor not only to put a limit upon the current iiow which passes through the device but actually assists in extinguishing such current flow and allows the disconnection of the circuit within the device to occur without violence. Such a device as I have above described may, therefore, be employed in limited installation space and without danger oi causing faults by its operation.

If the device is subjected to very low fault current the fuse element operates without the current having increased to such a value as to bring the automatic resistance into action. For example, in the device shown in Figure 6, the normal RMS load current may be 1/ 10 ampere. The instantaneous value oi current on low fault current conditions starts out to reach a peak of from 1 to 2 amperes, such as occurs in the primary circuit of a' current transformer when the secondary terminals are short circulted. The fuse element such as the silver wire 5l melts, but the tungsten wire l0 is not heated to any appreciably effective temperature and it does not come into action to reduce its conductivity. Interruption occurs at the fuse element by liquid quenching and deionization of the arc in the normal manner without developing any violence in pressure which would require the cap i! to be blown on.

Assume, however, that there is a low resistance fault. Then, although the normal RMS load current may be only 1/ 10 ampere, the instantaneous value of current starts out to reach a peak of say 10,000 amperes, such as occurs in the primary circuit of a current transformer in case the primary terminals are short circuited. Immediately the fuse element melts, and the arc starts at the fuse terminals. The rapidly increasing current passes through the arc and through the tungsten wire. In fact, the tungsten wire begins to increase in resistance by its automatic action before the fuse element is melted. 'I'he ohmic resistance increase of the tungsten wire is negligible in the total circuit resistance and is not effective in holding down the current. Arcing at the fuse element increases rapidly and heating of the tungsten as rapidly results in oxidizing tempera ture for the tungsten with the evolution of oxygen from the calcium carbonate. The chemical combination between the oxygen and the tungsten rapidly reduces the cross-sectional area o! the tungsten, thereby greatly accelerating the increase in resistance. This proceeds with great rapidity, to the order of l0 megohms, that is, substantially an insulator, and halts the rise of current in its own path which has been proceeding towards a flow of 10,000 amperes, The increase of resistance is so rapid as to halt the increase of current flow and immediately reduce it to zero after it has reached an instantaneous value of not greater than 500 to 600 amperes. The actual interruption oi' current dow may occur either at the fuse Il or within the tungsten wire resistance. During the rapid reduction in current caused by the rapid increase in the series resist- `ance element, the arc becomes unable to maintain itself and is quenched at the fuse terminals. It may be that the tungsten wire in approaching a substantially non-conductive condition, breaks into a series of tine arcs throughout its length, which arcs cannot be maintained by the available voltage and the arcs then become snufied out, but it is to be observed that if any appreciable arcing should occur through the resistance element the resistance of the path would immediately be reduced and the duty of interruption would then fall upon the fuse clement. Upon interruption of the current ilow, the resistance, which has been converted into substantially a non-conductor, and the interposed fuse liquid in the fuse element, prevent reestablishment of current now through the device. The fuse element with the retnctible terminal performs, in any event, the important duty of disconnecting the circuit, that is, moving the terminals of the circuit so far from each other, and interposing a dielectric, that the arc cannot be reestabliahed by puncture.

Due to the fact that the automatic resistance is dependent for its action upon current flow, the increase in resistance rapidly overtakes the increase in current flow and halts the release of energy in the fuse. The result is that the device operates with unusually low energy release. When the parts are properly proportioned the vent cap will not be blown off and no external disturbance is created. The disconnection or operation of the fuse may readily be observed through the glass sleeve i.

In the device shown in Figure 9, parts 1 and 2, I have illustrated an embodiment in which the fuse and the resistance are connected in series when the valve raises. Normally, the valve contact short circuits the resistance. In this construction the glass sleeve i has the ferrule 2 at its upper end and the cap 3 at its lower end cemented by suitable sealing alloy l to retain a suitable charge of dielectric arc extinguishing liquid 20. The spring i has a head 13 it its upper end coupling the same through a co ling il to the rod-like movable terminal 0J. The coupling 'il' has a socket at its lower end for connection with the flexible conductor 2l which shunts the spring l. Similarly, the flexible conductor 24 is connected to a socket at the lower spring head I5 to make connection to suitable stud H0, fitting in a socket in the cap member i, At its upper end the movable terminal or plunger has an arcing tip Il! to which are connected both the high tensile strength strain wire 8 and the silver fuse wire 1. At their upper ends the strain wire I and the fuse wire I are fastened to a removable arcing tip terminal member l I3 which is formed in the shape of a headed screw threaded into and extending through a hollow tubular stem member ill. The stem member Ill has a flange il! with the periphery thereof tapered of! to form a tapered valve seat like a poppet valve. Suitable relief openings lll are formed through the valve, otherwise the valve tends to close oil the space above it from the space below it by contacting with a tapered metal seat H1 which is formed as an annular inwardly extending flange on a sleeve or ring member ill that is threaded at its upper end into the main upper accenna ferrule 2. At its lower end the ring or sleeve ||0 is internally threaded to receive the reduced and threaded end of a "Bakelite fiber insulating sleeve H9. This insulating sleeve ||9 fits loosely within the glass sleeve l| and provides within its bore an arcing chamber which is substantially filled with the dielectric arc extinguishing liquid 20. The rodlike movable terminal 63 extends up through the bore of the tube IIS to a point adjacent the lower end of the hollow stern ||4. The sleeve ||9 at its lower end has a perforated plug |20 embracing fairly closely the lower end of the plunger terminal 63 and being provided with labyrinth grooves |22 to retard the flow of fluid through the space between the stem 63 and the opening in the plug |20. The perforated plug |20 is held in place at the lower end of the sleeve ||9 by a ring |23 seated partially in a.

groove formed on the inside of the sleeve ||9 and partially in the plug |20. A removable ring |24 on the upper end of the plug |20 provides a re.

leasable shoulder for purposes of assembly. The plug is preferably made of insulating material. The upper ferrule 2, which forms the external terminal, is provided with an extending radial flange |25 with a cylindrical extension |26, which may be formed separately and screw threaded in place, or which may be formed integrally if desired. At its upper end the cylinder |26 is closed by a cap |21 threaded into the open end thereof and provided with a vent opening |28 closed by a releasable vent cap |29 cemented in place. A spider member |30 mounted in the upperend of the cylinder |26 immediately belowthe closure |21 has a central opening |32 through which is extended a threaded stud |33 and held in place by a clamping nut |34. The stud |33, at its lower end, has a clamping flange |35. The stud extends through the neck |36 of a closure member |31. This closure member is internally threaded to receive the upper end of a fiber cylinder |38 which forms the container for the automatic resistance. unit 6b. 'I'he stud |33 thus clamps the closure member against thespider |30, holding by a fiber disc |39 perforated at its center to receive the guiding sleeve |40. The guiding sleeve |40 has a flange |42 immediately above the fiber disc |39 and forced into engagement therewith by the hollow rod of insulation |43. This hollow rod of insulation |43 abuts at its upper end against the flange |35 of the stud member |33 and at its lower end against a flange |42 of the sleeve member |40. The hollow rod is plugged off at |44 by an integral wall which serves as insulation between the lower end of the stud member |33 and the upper end of the sleeve member |40. The flanges |35 and |42 form connections for the ends of the resistance wire I0, which resistance wire is made of tungsten or the like. 'I'he space between the sleeve |38 and the hollow rod |43 is lled with marble dust |2 to cooperate with the tungsten wire l0. The stud member |33 and the sleeve |40 are coupled together against rotary motion by pins 46| 46. The hollow stem 4 within which the fuse and strain wire 1-3 are disposed, is guided within rthe sleeve member |40. is connected to the upper end of the metal sleeve |40 by a coiled flexible conductor |41 which, at its upper end, is connected by soldering to a spring clip forced into the upper end of the sleeve l 40 and there soldered in place. The lower end of the flexible conductor |41 is soldered in The upper end of the terminal screw ||3 and the internal ring I I8 are covered by rings |50 and |52 formed of ilber or the like. 'I'he rings |50 and |52 are held together by press flt, and the threads on the ring |52 engage the internal threads of the metal ferrule 2, as shown in Figure 9, part 1. A series of annular cork washers |53 are disposed between the upper end of the resistance unit 6b and the inner wall of the chamber formed by the sleeve |26. These washers close oil the annular space around the resistance element 6b and tend to limit the escape of liquid and gas to the upper metal cap member or closure |31.

, The circuit made through the device is as followsr--From the lower terminal 3 through the stud ||0, ilexible conductor 24 to the movable plunger terminal 03 which is connected to the lower end of the fuse and strain wire 1 and 0. Thence the circuit proceeds through the fuse and strain wire to the upper terminal member H3, then the circuit divides, extending in one path down through the hollow stem member ||4 which is made of metal, the flange H5, to the valve seat ||1, ring member ||9 and this, in turn, is in contact with the upper fuse ferrule 2; the other path, which is of higher resistance, extends through the flexible lead |41, sleeve |40, resistor l0, terminal |33, and through spider |30, sleeve |26, to ferrule 2.

Upon a Arise in current which melts the fuse wire and strain wire 1 and 8 and releases the terminal 63, an arc is formed Within the stem ||4, but as this is of metal the arc will immediately tend to be shunted by the metal and extend only between the lower end of the stem member ||4 and the arcing terminal H2.

The blowing of the fuse within the metal stem ||4 provides a unique and useful action. As the .fuse is vaporized the metal vapor is projected against the relatively cold walls and much of it is condensed and remains on the walls. It is therefore taken out of the arc because the metal stem affords a low resistance path which shunts the arc. 'Ihe 'pressure which is generated by such blowing raises the valve, lengthening the gap between the lower end and the arcing tip ||2, thus taking a large part of the metal vapor out of the arc and almost instantly introducing a part or all of the gap which was removed by the arc being shorted by the tube. At the same time, the valve ||5 leaving its seat tends to draw one or more arcs at this place,

.raise it, passes out the gap between the rim of the valve and the surrounding walls, particularly the flared wall of the insulating ring |52,

tending to extinguish the arc or arcs from the` rim of the -valve ||5 to the seat II1. The flared annular space between the valve ||5 and ring 52 provides an expansion nozzle for the gases and vapors,` tending to chill the valve |.I5 and also holding the main arc between tips and 2 centralized. The liquid filling extends to approximately the lower end of the hollow valve stem ||4 as indicated in Figure 9, where it is promptly acted upon by the pressure and heat of the arcto produce the action above described. The movable terminal ||2 also begins to descend. adding its effect 'to those above described.

'I'he result of the above action is to open the shunt originally existing about the resistance iii, causing said resistance to be in series with the main arc between the tips and H2. The circuit which contains the resistance I6 will immediately assume the burden of carrying the current, the arc or arcs between the flange or valve ||5 and the seat ||1 being extinguished and the current being all passed through the tungsten wire i0. Immediately upon the current passing through the wire it begins to heat up, and the automatic action of reducing its own conductivity by chemical reaction occurs. Meanwhile, the terminal member 63 is receding under the action of the central spring 9, and while the above action may take place in so short a time as to permit the stem 63 to move downward only a short distance, its motion begins to be accelerated and by the time that the current flow is interrupted, suillcient distance and sufflcient dielectric liquid intervene to prevent restrilning of the arc, even though the valve member with its hollow stern ||4 drops downwardly. The shunt path containing the resistance Wire l0 is as followsz-From the hollow valve stem ||4 through the flexible conductor |41 to the metal sleeve |46, through the ilange |42 to the lower end of the wire resistance I6, then to the upper terminal of the wire i0 which comprises the stud |33, through the spider |30, metal cylinder |26, to the flange |25 of the upper ferrule 2.

It` is to be observed that the action of the valve in raising from its seat and interposing resistance by the projection of fluid ilow between the valve and its seat is designed to occur with great rapidity, since it is desirable to switch the resistance into the circuit and extinguish the connection between the valve ||5 and the seat ||1 in a fraction of a half-cycle.

The main arc between the arcing tip ||2 and the lower end of the hollow stem ||4 is not the one which is affected to effect the switching operation. It is the arc which tends to be drawn between the members ||5 and ||1 as the valve and its hollow stem rise. Since arc extinguishing liquid is forced with considerable violence through the narrow space in which this arc must exist, the said arc, which is established only upon said separating operation, has very little time to heat the adjacent parts or to establish a body of conducting vapor, with the result that it is quickly extinguished, although the main arc between the tip |i2 and the lower end of the hollow stem il4 persists. The circuit is then subject to the two interrupting actions in series, namely, that of the main arc and of the automatically increasing resistance. After the resistance has been switched in series with the arc of the fuse, the operation is as described in connection. with the previous embodiment.

The hollow valve stem may have a constricted outlet such as |2| through the side walls, preferably near the top, to permit some of the gas to escape and let the metal vapor occupy the space.

In fact, the tube ||4 may be extensively perforated so as to form chiefly a screen or basket, as shown in section in Figure ll, to catch the metal vapors and condense them. The arc within the tube ||4 is merely incidental to the use of a fusible link and the fusible link is a means for detecting excessive rise of current and for mechanically releasing the movable parts.

In the device of Figure l0 and as indicated in the diagram of Figure 3, the resistance element 6c is in a shunt circuit and is switched in upon blowing oi' the fuse element 6c. It may be completely out ot circuit, normally, and in that case a short arc or a movement o! the terminal |66 may bring it into circuit.

y In the device shown in Figure l0 the upper ierrule 2 has an extending flange |25 which, in conjunction with the metal sleeve |26 and the closure |21 forms a chamber at the upper end of the main glass sleeve The lower end of the device shown in Figure is substantially identical with the lower end of Figure 9, part 2, in that the spring 9 and the shunting flexible conductor 24 are connected to the lower ferrule 3 which closes the bottom cf the glass sleeve The upper end of the spring is anchored through a suitable head 13 to a coupling 14 to which is connected a stud member |55 bearing a removable arcing tip |56. The strain wire 6 and fuse wire 1 are connected to the removable tip |66 as heretofore described. The strain wire has a connection by way of a cross pin, giving a limited degree of universal motion and the coiled fuse wire 1, which is preferably made of silver, is laid in a slot extending endwise of the tip |66. At the upper end of the wires 1 and 6 a similar connection ismade to the terminal |51. 'I'he terminal |51, at its upper end, is connected to a number of parallel flexible strands |66 and they, in tum, are connected to a socket |56 of the terminal member which ends in the stud |66, clamped by means of a nut |62 to the spring spider |63. The spring spider |63 seats in a recess in a perforated plate |64. The plate |64 is threaded internally in the brass sleeve |26, thereby making connection with the external terminal, namely, the ferrule 2.

The resistance element 6c is housed within a sleeve of insulation |65 which, at its upper end. is closed by a head or plate member |66, having a flange for piloting the sleeve and head together as shown at |61. The head |66 lies immediately below the plate or disc |64. The opposite end of the housing sleeve |65 is closed oil' by a similar head member |68 which has a piloting flange |66 for holding the Bakelite sleeve |65 in definite relation to the brass heads |66 and |66. A spac ing sleeve of fiber |10 has an inwardly extending flange |12 threaded onto the upper end of a fiber liner |13, the lining sleeve being threaded into the ferrule 2 and the lower end of the lining sleeve |13 extends down below the liquid level, as shown in Figure 10. A thin tubular metal sleeve |14 lies inside the upper part of the lining sleeve |13 and it is connected as by means of a shoulder soldered to the lower head |66. At its lower end the metal sleeve or cylinder |14 has a relatively thick guiding ilange |15 which ts rela- -tively loosely around the stem |55 of the movable terminal. An insulating sleeve |16 lies within the metal sleeve |14 and extends from the upper head |66 of the resistance unit 6c down to the flange |15 thatis connected to the lower head |66 of said resistance unit 6c. A cylinder of porous insulating material surrounds the upper end of the movable terminal |56|56, the fuse and strain wires 1 and 6, respectively, the upper terminal |51, flexible conductor |58, and communicates through @clamping ring |11 with the space above the disc |64, This aluminum oxide cylinder |16 is held in plhce by the threaded clamping ring |11 and forms, in effect, an arcing chamber. The cylinder of aluminum oxide is porous and the lower end thereof dips into the arc extinguishing liquid 20. It constitutes a wick for maintaining a tions.

supply of the dielectric arc extinguishing liquid throughout its length. The aluminum oxide cylinder |18 is preferably o! such size as to fit relatively closely about the terminals and connec- It is of very high resistance to current flow and its function is to furnish both a refractory tubular wall and to serve as a wick for the liquid dielectric 20. The tungsten wire I is wound about the Bakelite sleeve |16, out of contact with the same, and the wire is surrounded by the filling l2 of marble dust or the like. T he ends of the wire I0 are connected to the head members |66 and |68. The head member |68 is connected to the guiding flange |15 and the upper head member |66 is connected to the external terminal or ferrule 2.

Upon the occurrence of fault current the wires 1 and 8 become fused and an arc is established.

' Pressure is generated thereby within the aluminum oxide sleeve |18. 'I'he heat of the arc immediately evolves a gaseous medium from the liquid contained in the porous wicklike member |18 and such gaseous medium acts to expel the vapor of the fuse and the arc gases upwardly into the chamber |19 above the disc |64. At the same time the movable terminal begins to be retracted into the liquid. The upper terminal |51, its flexible leads |58 and the connecting spider |63 are expelled, thereby rapidly increasing the length of the arc and tending to extinguish the arc. As the resistance of the arc is thereby increased, suflicient potential difference between f/face.

the ends of the arc will occur to cause the current to flow from the lstem |55|55 to the metal guiding flange |15, which then switches the resistance |0 in parallel with the arc. The division of current, together with the extinguishing effect of the arc extinguishing medium, rapidly transfers the current flow to the resistance I0. Travel Lof the terminal iss-|56 te a point below the guiding ange |15, if the arc has not previously been extinguished, will definitely extend the current ow through the resistance`V wire IB, and it thereupon automatically acts to efface itself as a conductor and to substitute a non-conducting oxide or other compound, y. terminating further current flow.

In this embodiment the resistanceV element 6c is sealed ofi' completely from the liquid, although the liquid is carried to a level up to the top of the unit by the porous aluminum oxide cylinder |18.

After the current is switched to the resistance I0 its operation is as heretofore described.

The porous or absorbent cylinder |18 holds the liquid in definite position about the fuse, even though the actual level of the free liquid may be higher or lower. The free liquid level should be high enough to wet the lower end of the porous or wick-like member |16. This member need not be a vcomplete tube to be effective. The preferred form is a self-sustaining refractory insulating member charged with arc extinguishing material which is evolved or released from the member by the arc, the medium being freely released, preferably through the body'7 or struclture of the member and not only from the sur- Other absorbent media may be employed, such as lava, asbestos, kieselguhr and the like.

In each of the above forms the releasable vent cap may be blown off if excessive pressure should be generated within the device. It is present as a safety feature not required on normal operation. The device may be recharged after-,each

operation, this being done preferably at the factory in order to be assured of proper assembly and to secure freedom from impurities. After the device has operated to interrupt current flow, it is to be removed from the circuit. Its operation may readily be determined by inspection, this being possible at a distance in view of the employment of the glass sleeve, and the clear arc extinguishing liquid which is preferably employed. In each case, after the operation of the device, the fuse terminals are separated so as to disconnect the circuit and to provide a space which is then filled by a liquid dielectric of a high order.

It will be seen that the silver fuse wire is designed to act qualitatively, that is, to blow and form an arc when a definite current is reached or exceeded, whereas the tungsten wire is intended to act quantitatively, that is, to begin to reduce its conductivity when a definite current flow is reached or exceeded. When the silver fuse wire blows it forms an arc. When the tungsten wire reaches the temperature at which it begins to combine chemically with the reagent, for example, oxygen, it begins rapidly to increase its resistance. The above decrease of conductivity is quite aside from the change of resistance due to the temperature coefficient of the metal.

It is to be understood that I do not intend to be limited to silver wire and tungsten wire, respectively. Any metals which have substantially the capabilities required to perform the services of these two wires I consider to be equivalent. Certain alloys of copper, which have a high resistance to corrosion and good conductivity, may be employed instead of silver, or other metals or alloys of which I am not now informed may be substituted to perform the service of the silver fuse wire. Likewise, certain other metals such as tantalum, osmium, and perhaps others, may be employed in the place of the tungsten lwire. Instead of the combination of oxygen with the metal of the resistance wire, some other reagent or active negative element or radical may be employed.

It is to be noted that the oxidation of the tungsten wire, or its equivalent, accelerates the heating. It is always desirable to have the tungsten or equivalent wire in relatively small strands in order to secure a relatively large ratio of surface to cross-section, to accelerate the action.

In the 'graph of Figure 5 I have shown the fault as occurring at the instant that the voltage crosses zero, so as to secure conditions which would lead to the greatest rate of current increase. This is the condition of greatest severity, and if the device can take care of such conditions it is fully capable of taking care of less severe conditions.

In connection with the fuse 5, it is not absolutef ly essential that the arc extinguishing liquid be employed in every case, but it is highly desirable to employ the same as a liquid dielectric between the terminals which open the circuit.

The fuse element measures the overload and initiates the circuit interrupting action. After the fuse has once melted the circuit is interrupted, whether the current rises further or not. If the current flow increases upon the establishment of the arc at a rate which indicates a high peak value, then the automatic resistance begins choking the current flow in proportion to the rate of increase. The rate of increase of current flow from zero towards maximum is indicative of the seriousness of the fault, other things being the same.

I am aware that so-called "chemical fuses" have heretofore been proposed for use in low tension circuits. Examples of such fuses are disclosed in Hadaway Patent No. 620,309, and Sachs Patent No. 522,232. These fuses are intended to interrupt circuit ow without an arc by chemical action between the metal of the fuse and a cooperating compound, which action is initiated by the attainment of a certain temperature.

In actual practice, the action of such fuse is not all that may be desired for either low tension or high tension use, because of two defects which my present invention cures.

First, such chemical fuses when subjected to marginal operation will deteriorate, because a partial action may be initiated and not completed. Or, if the fuse stands for a time just below the point where active chemical action is to be initiated, the fuse likewise deteriorates. In either case, the fuse rating is changed and the fuse thereafter will not carry full power load, and is quite unreliable.

Second, such "chemical fuses frequently, and especially on marginal operation, or by slow deterioration, will not convert the metal to complete non-conductivity. The fuse then will prevent any substantial flow of current because of the high resistance of the body thereof, but no actual gap is produced, and the fuse will still transmit potential. 'I'his is of no great consequence where only low potential is involved, but upon high potential circuits, or where high potential is impressed upon the fuse, such transmission of potential is highly undesirable, and is dangerous. Such partial conductivity may also result from the action resulting from a short circuit. The heat evolved may be great enough to melt the resulting compound, and thus produce a path of partial conductivity through the melted residue.

My invention overcomes both of the above defects, and provides a fuse suitable for any potential and particularly useful for high potential currents where the requirements are most severe. The manner in which this is done is fully describedabova but may be recapitulated in part as follows:

The fusible conductor l (or b, lc) which is the current measuring element is designed to and will melt at a current now through the device well below that at which any marginal operation of the chemical fuse 6 (or ib, 6c) can be initiated. Hence, deterioration of the chemical fuse does not occur.

Next, the melting of fusible conductor 5 (or 5b, 5c) produces a gap in the metallic circuit whereby, if and when the "chemical fuse operates and the current flow is interrupted by its action, the chemical fuse is completely disconnected, so that potential leakage through said "chemical fuse is rendered harmless. Whether the current flow is great enough to operate the chemical fuse or not, the melting of the fusible conductor fuse causes a gap and resultant disconnection.

By the above unique cooperation of a fusible conductor operating at a suitable low value of current flow as compared with the value of current flow required to initiate operation of the chemical fuse, a wholly new utility or combination is provided, not only in the production of a reliable eilicacious fuse, but, in addition, a selective operation is produced in that for overload currents the fusible conductor may act alone to interrupt current now and produce a disconnectaoco, 12o

Upon short circuit currents, both fuses operate to extinguish a now oi' current which may be so large that the fusible conductor fuse may be incapable of interrupting it without the aid of the chemical fuse; and the fusible conductor fuse then disconnects the circuit to prevent potential leakage which the chemical fuse" may not be able to do.

Thus the fusible conductor fuse protects the chemical fuse" from deterioration and disconnects it if it operates, while the chemical fuse" on the other hand reduces the heavy load on the fusible conductor fuse and permits it to perform its interrupting and disconnecting function, and the two fuses in addition act selectively.

I do not intend to be limited to the details shown and described.

I claim:

1. A protective device comprising a fuse element having automatically separable terminals, said fuse element having a link adapted to fuse and form an arc and permit said terminals to separate upon the occurrence of overload and a resistance element having a stationary resistor permanently increasing its resistance upon the occurrence of a predetermined current flow therethrough and adapted to be connected in series with the arc to control the energy release in the arc.

2. A protective device comprising a fuse element and a resistance element connected in series, said resistance element having means to cause it to increase its resistance permanently substantially without arcing upon the occurrence of a current of predetermined value through the device, said fuse element being designed to blow at a value of current substantially lower than said predetermined value.

3. A protective device comprising a fuse element and a stationary resistance element connected in series, said resistance element having means to cause it to increase its resistance permanently upon the occurrence of a current of predetermined value through the device, said fuse element having a fuse link provided with separable terminals and means to separate the fuse terminals upon the blowing of the link so interpose a definite gap in the circuit, the fuse link being designed to blow at a value of current flow which will not cause the resistance to be permanently changed.

4. A protective device comprising a fuse element .having a fusible link, a self-increasing resistance element having a resistor associated with the link, and means for automatically transferring current ow from the fuse element to the resistance element upon blowing of the link, said means introducing a permanent gap in series with the resistance element.

5. A protective device for an electric circuit, comprising a fuse element having a fusible link, movable terminal means, a self-increasing resistance element having a resistor which acts by excessive current now to increase its resistance permanently, said movable terminal means switching said resistance element serially into the circuit upon the blowing of the fusible link.

6. In a protective device, a fuse, and a refractory current limiting resistance comprising a conductor and a normally inert reagent, said conductor being of low ohmic value which upon a rapid increase of current ilow through the fuse n permanently increases its resistance to a high value without the formation of an arc.

7. In a protective device, a fuse, and a refractory current limiting resistance comprising a. conductor and a normally inert reagent, said conductor being of low ohmic value which upon a rapid increase of current flow through the fuse permanently increases its resistance to a high value without the formation of an arc, and a single tubular fuse housing having external terminals for enclosing said fuse and current limting resistance.

8. In a fuse, a fusible link and a surrounding sleeve comprising an absorbent insulating material wet with a liquid arc extinguishing material said sleeve comprising a porous granular refractory body. 9. In a fuse device, a fusible link, a surrounding sleeve of porous refractory insulation wet with a liquid arc extinguishing liquid and a sleeve of brous insulation capable of withstanding high internal pressures embracing said porous sleeve.

10. In a fuse device, a fusible link and a surrounding sleeve of aluminum oxide wet with arc extinguishing liquid.

11, In a fuse device, a fusible link, terminals for the link, means for moving one of said terminals away from the other .upon blowing of the link, a body of liquid into which said movable terminal is moved, and a wcklike member extending alongside the fuse, a part of said member extending into the bodyof liquid and absorbing liquid therefrom.

12. In a fuse device, a fusible link, terminals for the link, means for moving one of said terminals away from the other upon blowing of the.

link, a body of liquid into which said movable terminal is moved, and a wicklike sleeve embracing a part of the link and the movable terminal and having a portion thereof in contact with the liquid.

13. In a device of the class described, a sleeve of insulation having external terminals at its ends, a fusible link in said sleeve connected at one end to one of said terminals, a limiting resistance within said sleeve, said resistance having terminals one of which is connected to the other external terminal, a spring within the sleeve anchored to the other end of the link and to the other end of the resistance and means within the sleeve for flxedly supporting said other end of the resistance and forming an anchorage for the adjacent end of the spring.

14. 'In combination, a fuse element, an oxidizable resistance element of relatively low initial resistance, means for connecting said elements in an electric circuit, means for permanently increasing the resistance upon predetermined temperature rise by flow of current therethrough, the fuse element being melted upon increase of current flow to a predetermined value, said value being less than the value ofvcurrent flow at which said resistance element permanently changes its value, and means to conduct through the resistance element the flow of current through the arc which occurs upon blowing of the fuse and means for shielding the resistance element from the arc occurring upon the blowing of the fuse. j

15. In combination, a fuse element, an oxidizable resistance element of relatively low initial resistance, means for connecting said elements in an electric circuit, means for permanently increasing the resistance upon predetermined temperature rise by now oi' current therethrough, the fuse element being melted upon increase oi current flow to a predetermined value, said value being less than the value of current ow at which said resistance element permanently changes its value, means to conduct through the resistance element the ilow of current through the arc which occurs upon blowing of the fuse, said moans acting upon blowing of the fuse to switch the current flow of the arc through said resistance element.

i6. In combination, a fusible conductor and a substantially infusible conductor connected in a parallel branch, terminals for said conductors, a compound in thermal contact with the infusible conductor, said compound being adapted to be heated by said second conductor to evolve a reagent which combines with said second conductor to render it less conductive. and spring means for increasing the resistance of the circuit including the arc formed upon fusion of said nrst conductor to cause the current to pass to said parallel branch.

17. In a device of the class described, the combination of a fuse melting at a predetermined current value, and a resistance melting at a relatively higher current value, said fuse having means to extinguish the arc caused by blowing of the fuse, and said resistance having means to render it substantially non-conductive without arcing upon rise in current flow to said relatively higher value, said fuse and resistance cooperating to reduce the current flow through the device and means to shield the resistance from the influence of the arc.

18. In a device of the class described, the combination of a pair of conductors adapted for connection in a circuit, the first conductor melting at a predetermined value of current flow, and the second conductor melting at a relatively higher value of current, upon increase in current flow the first conductor melting and forming an arc, means to separate the terminals of the arc independently of the second conductor, means to deionize the arc and interpose a dielectric between the terminals thereof, and means in thermal contact with the second conductor adapted upon being heated by said conductor by said relatively higher value of current to release a reagent which combines with the metal of the conductor, and reduces the same to a non-conductor.

19. In a device of the class described, a sleeve of glass having external circuit terminals upon the ends thereof, a conductor disposed within said sleeve, said conductor upon excessive ilow of current therethrough being reduced by chemical action to a non-conductor, a fusible conductor disposed within the sleeve, said latter conductor having terminals, one of which is movable upon the melting of said fusible conductor, a liquid dielectric medium within said sleeve which is introduced into the space between said terminals upon the movement of said movable terminal, and means connecting said conductors to each other and to said external terminals.

20. rIn combination in an electric circuit, a pair of conductors, terminals for said conductors, one of said conductors having spring means for producing separation of its terminals only, and a normally inert chemical reagent activated by heating of the other conductor to combine with the materialthereof to produce a substantially non-conducting compound, said other conductor being heated to the degree required to activate said reagent only after said one conductor is fused.

21. In an electric circuit, a tungsten wire and a silver wire connected in parallel branches, a mass of limestone in contact with the tungsten wire, and a spring for extending the arc caused upon fusion of the silver wire, and means for shifting current iiow from the arc to the tungsten wire.

22. In an electric circuit, a tungsten wire and a silver wire connected in parallel branches, a mass of limestone in contact with the tungsten wire, a spring for extending the arc caused upon fusion of the silver wire, means for shifting current ilow from the arc to the tungsten wire, and a body of dielectric liquid adapted to be interposed between the terminals of the fused wire upon cessation of the current flow.

23. In an electric circuit, a circuit protective device comprising a fuse which blows upon a predetermined rise of current through the device, a conductor which permanently changes its resistance only upon a higher rise of current than said predetermined rise, blowing of said fuse resulting in an arc, means to separate the terminals of the arc, an arc extinguishing medium for said arc, and means for conducting the current flow through said conductor upon blowing of the fuse.

24. The method of controlling the energy release in an arc, which comprises conducting the flow of current which sustains the arc through a refractory conductor, heating said conductor by such current flow to a temperature at which the substance of the conductor is active chemically, evolving by said heat a chemical reagent, combining said reagent with said conductor to reduce it to a substantially non-conductive state, and simultaneously extending the length of the arc.

25. In a device of the class described, a fuse housing, comprising a tubular sleeve having external circuit terminals forming closures for the sleeve, a resistance chamber in said housing but out of communication therewith, a refractory resistance conductor in said chamber, a compound in said chamber adapted to release a reagent for combining with the conductor, a fusible link in said housing, a movable fuse terminal, a spring for moving said fuse terminal, and a body of arc extinguishing material in the housing, said resistance conductor being included in series with the arc formed upon blowing of the fuse for controlling the energy released in the are.

26. In a device of the class described, a fuse housing, comprising a tubular sleeve having exteral circuit terminals forming closures for the sleeve, a resistance chamber in said housing, a refractory resistance conductor in said chamber, a compound in said chamber adapted to release a reagent for combining with the conductor, an arcing chamber, a fuse in said arcing chamber, a movable terminal for one end of the fuse, a spring for moving said movable terminal independently of said resistance conductor, and a body of arc extinguishing liquid in said housing for acting upon the arc in said arcing chamber when the fuse blows, said refractory resistance controlling the energy released in said arc.

27. In a device of the class described, a fuse housing comprising a tubular sleeve having external circuit terminals forming closures for the sleeve, a resistance chamber in said housing, a refractory resistance conductor in said chamber,

a compound in said chamber adapted to release a reagent for combining with the conductor, an arcing chamber having a movable closure member at one end forming a i'use terminal, a rodlike fuse terminal projecting into the arcing chamber from the other end, an arc extinguishing medium for acting upon the arc formed upon blowing of the fuse, and a fuse between said terminals.

28. In a device of the class described, a fuse housing comprising a tubular sleeve having external circuit terminals forming closures for the sleeve, a resistance chamber in said housing, a refractory resistance conductor in said chamber, a compound in said chamber adapted to release a reagent for combining with the conductor, an arcing chamber having a movable closure member at one end forming a fuse terminal, a rodlike fuse terminal projecting into the arcing chamber from the other end, an arc extinguishing medium for acting upon the arc formed upon blowing of the fuse, and a fuse between said terminals, said movable closure member having a central arcing tip for controlling the position of the arc, said movable closure member controlling the current iiow through said resistance.

29. In a device of the class described, a fuse housing comprising a tubular sleeve having external circuit terminals forming closures for the sleeve, a resistance chamber in said housing, a stationary refractory resistance conductor in said chamber, a compound in said chamber adapted to release a reagent for combining with the conductor to cause apermanent increase in the resistance of the conductor, a fuse in another part of said housing, a movable terminal for the fuse, an arc extinguishing medium for quenching the arc, a spring for said movable terminal, and a vent from said resistance chamber to atmosphere independently of said fuse containing part of the housing.

30. In a device of the class described, a fuse housing comprising a tubular sleeve having external circuit terminals forming closures for the sleeve, a resistance chamber in said housing, a refractory resistance conductor in said chamber, a compound in said chamber adapted to release a reagent for combining with the conductor, a fuse in another part of said housing, a movable terminal for the fuse, an arc extinguishing medium for quenching the arc, a spring for said movable terminal, and a vent from said resistance chamber to atmosphere independently of said fuse containing part of the housing, and a releasable vent for the part of the housing containing the fuse.

31. In a device of the class described, a husing, external terminals on said housing, a liquid quenched fuse in one part of the housing, an oxidizable resistance in another part of the housing, connections for said fuse and said resistance to said external terminals, and independent vents from said housing to atmosphere for said fuse and for said resistance.

32. In combination, a main tubular housing having external circuit terminals, a fuse at one end of the housing connected to one of said terminals, a movable terminal connected to the other end of the fuse, a spring in the housing connected at one end to said movable terminal, a resistance unit comprising a separate tubular housing within the other end of said main housing, external terminals on said separate housing, an automatic resistance member within said separate housing, a charge of suitable compound within said latter housing for combining with said accenno resistance, said spring being anchored at its other end to one of the terminals of the resistance unit, the other end of the resistance unit being anchored to the adjacent main housing terminal,

said fuse being adapted to melt immediately upon the attainment of a predetermined value of current flow, said resistance member being adapted to react with said compound only after said fuse is melted.

33. In combination, a main tubular housing having external circuit terminals, a fuse at one end of the housing connected to one of said terminals, a movable terminal connected to the other end of the fuse, a spring in the housing connected at one end to said movable terminal, a resistance unit comprising a separate tubular housing within the other end of said main hous ing, external terminals on said separate housing, an automatic resistance-member within said separate housing, a charge of suitable compound within said latter housing for combining with said resistance, said spring being anchored at its other end to one of the terminals of the resistance unit, the other end of the resistance unit being anchored to the adjacent main housing terminal, a tubular arcing chamber for said fuse, and arc extinguishing material for said fuse, said fuse being adapted to melt immediately upon the attainment of a predetermined value of current flow, said resistance member being adapted to react with said compound only after said fuse is melted.

34. In a device of the class described, a sleeve of insulation, ferrules on the ends of the sleeve forming external circuit terminals, one of said ferrules having a tubular extension, an annular resistance vunit disposed in said extension, said unit comprising a resistor, a fuse substantially in axial alignment with said unit, a spring disposed in said sleeve, a movable fuse terminal connected to said spring, a second fuse .terminal ccnnected to one end of said resistor and to the adjacent ferrule.

35. In a device of the class described, a sleeve of insulation, ferrules on the ends of the sleeve forming external circuit terminals, one of said l'errules having a tubular extension, an annular resistance unit disposed in said extension, said unit comprising a resistor, a fuse substantially in axial alignment with said unit, a spring disposed in said sleeve, a movable fuse terminal connected to said spring, and a second fuse terminal connected to one end of said resistor and to the adjacent ferrule, said unit having a central opening within which a portion of said second fuse terminal is disposed, said terminal being movable in said opening under the fluid pressure occasioned by blowing of the fuse.

36. In a device of the class described, a sleeve of insulation, ferrules on the ends of the sleeve forming external circuit terminals, one of said ferrules having a tubular extension, an annular resistance unit disposed in said extension, said unit comprising a resistor, a fuse substantially in axial alignment with said unit, a spring disposed in said sleeve; a movable fuse terminal connected to said spring, and a second fuse terminal connected to one end of said resistor, and to the adjacent ferrule, said unit having a central opening within which a portion of said second fuse terminal is disposed, said terminal being movable in said opening under the fluid pressure occasioned by blowing of the fuse, said last named terminal serving to switch all the current through the resistor.

37. The method o! permanently interrupting current flow in a circuit, which consists in vaporizing one portion of the circuit. oxidizing another portion of the circuit to interrupt current flow and replacing a third portion of the circuit by a dielectric to prevent reestablishment of current ow.

38. The method of permanently interrupting current flow through a circuit, which consists in vaporizing one portion of the circuit to form an arc, oxidizing another portion of the circuit to reduce the current flow through the arc, so that it can be easily extinguished, and replacing a third portion of the circuit with a dielectric to prevent reestablishment of current flow through the circuit.

39. The method of permanently interrupting current ilow through a branched circuit, which consists in vaporizing a portion of one branch to form an arc, shifting a portion of the current from this iirstv branch to a second branch, so that the arc is easily extinguished in the rst branch, oxidizing a portion of the second branch into an insulating compound to interrupt current flow through it, and replacing an unbranched portion of the circuit by a dielectric to prevent reestablishment of current flow. l

40. The method of interrupting current flow through a circuit, which consists in vaporizingl one portion of the circuit and forming an arc, and oxidizing another portion of the circuit to reduce the current flow in the vaporized portion to a point where the arc will not sustain itself.

4l. In combination, a fusible link, an arcing chamber in which a portion of the arc is formed on fusing of the link, an arc extinguishing ma.- terial, and capillary means for bringing a portion of the arc extinguishing material and sustaining the same within the walls of the chamber.

42. In a liquid filled fuse, a fusible link maintained in a denite position, a liquid filling of arc extinguishing material, and means for maintaining the effective level of the arc extinguishing `material relative to the link independently of temperature variations of the medium surrounding the fuse.

43; The method oi removing metallic vapor from an arc evolved upon blowing of a silver fuse, which comprises condensing the metallic vapors upon an enclosing metallic wall.

44. In a device of the class described, a fusible link, a stationary sleeve embodying an arc extinguishing material surrounding the link, said sleeve being porous to permit the evolution of a 'l gaseous arc extinguishing medium from the body of the sleeve under the heat of the arc and a stationary sleeve of insulation surrounding said first sleeve for directing said gaseous medium end- Wise of the arc formed upon blowing of the link.

45. In combination, a resistance which is selfincreasing for currents above a predetermined value, a shunt about said resistance including a switch, a spring, and a fuse through which the spring holds the switch closed.

46. A protective device comprising, in combination, a fuse adapted to be melted and to form an arc, a resistance element which is self-increasing for currents above a predetermined value adapted to be connected in parallel with the arc when the fuse blows, a switch, and a spring released by melting of the fuse for operating the switch to conduct the entire current ilow through the re-y 

